Because of its versatility and practicality, Bluetooth Low-Energy (BLE) is becoming more popular as the wireless communication protocol for Internet-of-Things (IoT) applications. The recently finalized Bluetooth 5.0 standard enables a faster data rate, more versatile advertising channel interactions, and a more flexible communication range, which makes BLE radios more adaptive in IoT designs. However, state-of-the-art BLE designs still consume an average of 4-5 mW active power while commercial BLE SoCs consume more than 10 mW, limiting battery life ad placing a ceiling on the adoption of IoT devices. In applications that require extended battery life or self-powered operation via energy harvesting such as wireless body sensor networks (WBSN), implantable medical devices, and replaceable consuming electronics, BLE radios consume too much power to be adopted at a large scale. In such systems, ultra-low-power (ULP) radios with proprietary asymmetrical communication protocols are used to save power in the edge nodes while pushing all the computation and power into the base station. But these designs either suffer from a significantly lower data rate, more severe interference and multiple access issues, or an extra bulky aggregator. Thus, it's very beneficial to explore a way to further reduce the BLE radio's power consumption, especially the BLE transmitter (TX), and enable a standard compatible asymmetrical communication with a sub-Mw BLE TX in the edge-nodes and fully compliant BLE transceivers in a cellphone or tablet as the base station. It will not only save a significant amount of power and extend the lifetime of IoT state-of charge (SoCs), but could also help resolve the interference and base station issues in ULP wireless systems.
The bottleneck of further power reduction in BLE TX design mainly results from two building blocks: the local oscillator (LO) and the power amplifier (PA), which take more than 80% of the transmitter power consumption combined. Significant effort has been done in the phase-locked loop (PLL) design for BLE. And some state-of-the-art ADPLL designs have successfully broke through the 1 mW barrier. But due to the use of LC voltage-controlled oscillators (LCVCO) with quality factors <20, it is hard to reduce power any further, no matter the performance. A recent trend shows that more and more BLE designs prefer to use open-loop LCVCO designs with direct modulation, since its phase noise (PN) performance is more than enough for BLE. In normal cases, the LO PN requirement for a BLE TRX is determined by the receiver (RX) side due to the requirements in RX sensitivity, blockers, and reciprocal mixing, and it's always better to have a better phase noise. But for a BLE TX-only prioritized design, the phase noise limit for the local oscillator has not been defined yet. This is especially true if this transmitter is in an asymmetric network where the RX LO in the “base-station” is often overprovisioned with high phase noise tolerance. This disclosure will address this issue by giving a detailed analysis between phase noise and system level specifications for a transmitter. The relaxed phase noise limit for BLE TX will not only help bring down the transmitter power consumption to its physical limit, but also increases flexibility in BLE circuit design based on the application emphasis.
This section provides background information related to the present disclosure which is not necessarily prior art.